The invention relates to an injection member for a jet spray injection device through which device a dose of medicine is administered for subcutaneous or intramuscular injection.
It is often wanted to perform a subcutaneous injection of a medicine dose. The medicine is deposited in the subcutis tissue from where it subsequently finds its way to the blood. Especially diabetics have to frequently inject themselves with insulin to keep their blood glucose content under control. For this purpose a number of injection devices exist.
A conventional injection device comprises a syringe which is provided with a needle which has a length enabling it to penetrate the cutis and enter the subcutis where a dose of medicine is deposited by being pressed from the syringe out through the needle.
However, many people are reluctant to prick themselves with needles and although needles are made very thin and short an injection may still engender the above mention reluctance which may promote a user to cut down the number of injections to a level beyond the warrantable.
To overcome this needle phobia of the patient and to further reduce pain, various jet injection systems have been developed. Such jet injection systems have no needle, but instead use a spray nozzle through which the medicine is sprayed to give the medicine a speed enabling it to penetrate the cutis and be dispersed in the subcutis. However, dosing is difficult, in part due to the anatomical condition of the skin (cutis) where the first layer (stratum corneum) consists of dead keratinized cells. The layer is much more resistant to water penetration than to lipid penetration, and it forms a strong mechanical barrier, especially considering the thickness of the layer, which has a mean of 0.1 mm on the most of the body (thin skin). The stratum corneum is enlarged in a few specific areas (thick skin): e.g., the hand and the foot sole areas where injection normally is avoided. Beneath the stratum corneum lie various other layers of epidermis, with living skin cells, blood vessels, sensory nerve endings etc. Three epidermis is followed by the dermis which is mainly connective tissue. Then follows the subcutis (mostly adipose tissue and connective tissue). The size of the subcutis is very variable in the individual person and between persons. When using spray injection it is difficult to estimate how much of the medicine glances off from the dead cells at the skin surface and how much actually reaches the subcutis.